1. Field of the Invention
The invention relates to variable camber vanes used in turbomachines, particularly turbine engines for aircraft.
In order to improve the performance of a turbomachine likely to operate at different speeds, it is current practice to modify the inclination of certain vanes depending on the speed of the turbomachine. In a more elaborate arrangement it is also possible to vary the camber of some vanes depending on the speed of the turbomachine. Such variable camber vanes generally have a forward part termed the leading edge part, and a rear part termed the trailing edge part, which are pivotable relative to each other.
2. Summary of the Prior Art
Variable camber vanes are known having a fixed leading edge part and a movable trailing edge part, one example being disclosed in EP specification 0 274 293 in the form an air intake guide vane in which the leading edge part also forms a radial arm providing a connection between the air intake casing and the hub of an aircraft turbine engine.
Also known are variable camber vanes in which the leading edge part pivots and the trailing edge part remains stationary, for example as described in FR patent 2 325 831.
In addition, variable camber vanes are known in which the leading edge and trailing edge parts both pivot, as disclosed in U.S. Pat. No. 4,995,786.
In all of these types of vanes the improvement in performance obtained by adjusting the camber of the vane in the best possible way is adversely affected by the disturbances which manifest themselves in the fluid flowing along the side faces of the vane and at the level of the articulation. These disturbances originate from the spacing left between the leading edge part and the trailing edge part at the position of the articulation between them, and also from the discontinuity of the side surfaces of the vane at the position of the articulation, that is to say from the sudden change of direction of the tangent to these surfaces in the direction of fluid flow.
To overcome this drawback, EP specification 0 223 194 proposes placing a membrane of elastomeric or other material on each face of the blade, in the vicinity of the articulation. This solution prevents air from entering the space between the leading edge part and the trailing edge part, but a break in the continuity of the lateral surfaces of the vane in the vicinity of the articulation still remains.
In order to cool a vane, or alternatively to heat it, for example to remove ice which may possibly form on its surface, it is known to circulate a cooling or heating fluid inside the vane. However, this operation is complicated by the presence of the articulation between the leading edge part and the trailing edge part.
It is possible to inject the fluid separately into the leading edge and trailing edge parts. Injection into the fixed part of the vane poses no particular problem, but injection into the movable part of the vane requires a second circuit to pass, for example, through the pivots on which the movable part of the vane swivels in the casing. An example of such an arrangement is disclosed in FR patent 2 599 785.
The fluid may also be injected at a suitable place on the vane and made to circulate inside the vane from the fixed part to the movable part, or vice versa, but in this case fluid losses must be accepted because of the lack of fluid-tightness at the articulation position.
Accordingly, this solution is not suitable when it is necessary to de-ice air intake vanes of turbomachines such as those described in the aforementioned EP specification 0 274 293, since the hot de-icing air has to be taken from the compressor and leaks at the articulation position make an additional drawing necessary, which impairs the operation of the compressor.
The terminology currently used to denote each of the flanks of a vane should be noted. The flank which exerts a thrust on the fluid to be processed or which receives a thrust from it is generally concave and is denoted by the term intrados face. The flank opposite the intrados face is generally convex and is denoted by the term extrados face.